For hundreds of years engineers and scientists have recognized that the ambient thermal energy of the natural environment that is heated by the sun contains essentially unlimited amounts of free thermal energy. Unfortunately, all prior attempts to harness this natural heat energy and convert it into mechanical work with high power densities by a closed cycle heat engine utilizing the natural environment as its high temperature heat reservoir have failed. As a result of all of these unsuccessful attempts, thermodynamicists have concluded that such engines are impossible. However, it is important to point out that this negative conclusion is not based on any fundamental physical law of nature but rather on the unsuccessful attempts to construct such engines. Although the “second law of thermodynamics” is usually cited as the basic reason why such engines are believed to be impossible, the second law itself is based on unprovable “postulates” laid down by Kelvin, Clausius and Planck over a century ago when the principle of conservation of mass and energy was accepted without question. (See Thermodynamics, Charles E. Merrill Publishing Co., Columbus, Ohio, pages 147-153 by Joachim E. Lay.) The Kelvin-Planck statement of the second law of thermodynamics is: “It is impossible to construct an engine which, operating in a cycle, will produce no other effect than the extraction of heat from a single heat reservoir and the performance of an equivalent amount of work.”
By designing a cyclic heat engine that falls outside the operating conditions of the second law of thermodynamics (the premise) it is possible to harness the natural thermal energy of the environment at ambient temperature and convert a portion of it into mechanical work. One such heat engine is a simple toy called the “drinking bird” that can be found in almost any novelty shop. Although this engine is a closed cycle heat engine and uses the ambient environment as its high temperature heat reservoir, it operates by generating an artificial low temperature heat reservoir by evaporating water. Hence, it does not operate according to the prescribed conditions of the Kelvin-Planck statement of the second law of thermodynamics (the premise) and therefore cannot violate this law.
The basic thermodynamic operating principles of the drinking bird engine were analyzed by Carl Bachhuber in his paper, “Energy From the Evaporation Of Water, American Journal of Physics, Vol. 51, No. 3, March 1983, pp. 259-264. In particular, Bachhuber has shown that ordinary water can be used to extract an unlimited amount of natural thermal energy from the surrounding environment and convert a portion of it into mechanical work. Moreover, the specific energy of water that can be converted into useful mechanical work by this engine is approximately twice the specific energy available in automotive storage batteries. In a technical report issued by the Rand Corporation in August 1966, entitled A Simple Heat Engine of Possible Utility in Primitive Environments, Rand Corporation Publication No. P-3367, Richard Murrow proposed constructing larger versions of this engine for pumping water from the Nile river. A scaled up model of the basic drinking bird engine was constructed to a height of seven feet and found to be able to extract a considerable amount of natural heat energy from the ambient environment and convert a portion of it into mechanical work. In particular, the engine would be capable of extracting an unlimited amount of natural heat energy and convert it into an unlimited amount of mechanical work. (See, “The Research Frontier-Where is Science Taking Us,” Saturday Review, Vol. 50, Jun. 3, 1967, pp. 51-55, by Richard Murrow.) Obviously, engines such as these which operate by converting the natural heat energy of the environment at ambient temperature into an unlimited amount of mechanical work are not “perpetual motion machines.” In principle, larger engines of this type could be used to propel ocean going vessels indefinitely using ordinary sea water for generating an unlimited amount of mechanical work. Although this possibility is generally believed to be thermodynamically impossible, it is clearly not impossible. The existence of these engines proves that it is indeed possible, to extract natural heat energy from the environment at ambient temperature and convert a portion of it into mechanical work by creating an artificial low temperature heat reservoir (heat sink) below ambient. Unfortunately, all prior attempts have been impractical because they have very low power densities.
What has to be pointed out and emphasized regarding the possibility of violating the second law of thermodynamics is the creation of an artificial low temperature heat sink If any cyclic heat engine produces such a low temperature heat sink while it operates, it is, “strictly speaking,” operating outside the premise of the second law and therefore, cannot logically be subject to this law.
There is one type of heat engine that operates, as in the drinking bird engine, by converting natural heat energy in the environment at ambient temperature into mechanical work. They are known as “cryogenic engines.” Moreover, unlike the drinking bird engine, these engines operate at very high power densities. In this engine the working fluid is a liquified gas at cryogenic temperature, such as liquefied nitrogen at 77° K (−321° F.) which is the usual working fluid in cryogenic engines. They operate by compressing the liquified working fluid at cryogenic temperature to very high pressure (e.g., 500 Bar or 7,252 lbs/in2) by a hydraulic compressor. Since liquified gas has very low specific volume, relatively little mechanical work is consumed by compressing it. After it is compressed, it is fed into a heat exchanger maintained in thermal contact with the natural environment at ambient temperature. The high pressure liquefied working fluid entering the heat exchanger creates a significant temperature gradient across the thermal surfaces and a large amount of natural heat energy is extracted from the environment at ambient temperature and rapidly absorbed by the circulating compressed working fluid at cryogenic temperature. The liquefied working fluid is isobarically heated above its critical temperature (126.3° K in the case of nitrogen working fluid) and completely vaporized into a high pressure gas. The vaporization process results in a several hundred fold increase in its specific volume. In principle, the process is identical to that of feeding compressed water into the high temperature boiler of a conventional closed-cycle steam engine used for generating bulk electric power in a power plant. The compressed water absorbs the heat energy in the boiler and vaporizes into high pressure steam resulting in an increase of its specific volume. In the case of the cryogenic engine, the “boiler” is the natural heat energy in the natural environment at ambient temperature.
The cryogenic working fluid emerges from the heat exchanger as a very high pressure, superheated gas at about ambient temperature and fed into an expander where it is expanded down to a certain sub-ambient temperature above its critical temperature. Since the expanded working fluid still has a high pressure, it is fed into another heat exchanger in thermal contact with the natural environment where it absorbs additional natural heat energy and fed into another serially connected expander and expanded down to a sub-ambient temperature thereby converting the additional heat energy absorbed from the natural environment into additional mechanical work. Since the expanded sub-ambient gas still has a relatively high pressure, it is fed into another heat exchanger and expander to convert additional natural heat energy into additional mechanical work. This process of feeding the expanded gas back into a heat exchanger maintained in thermal contact with the natural environment at ambient temperature and expanded in another expander is continued in a series of serially connected reheating and expansion stages until the pressure of the expanded gas discharged from the last expander in the series reaches atmospheric pressure and exhausted into the open atmosphere. Since there is no natural heat sink to re-liquify the gas leaving the last expander, it is discharged into the open atmosphere as exhaust gas. The engine can only continue to operate by continuously feeding in new liquified gas at cryogenic temperature into the compressor. Thus, all prior art cryogenic engines operate by compressing a liquified gas to very high pressure and feeding it into a serially connected plurality of heat exchangers and expanders that extracts natural heat energy from the environment at ambient temperature and converts a portion of it into mechanical work in an open cycle. Since they operate by consuming liquified working fluid to generate mechanical power, they are similar, in principle, to internal combustion engines used for propelling conventional automobiles because these engines consume gasoline to keep operating. (The operating details of prior art cryogenic engines can be found in U.S. Pat. No. 3,451,342 filed Oct. 24, 1965 by E. H. Schwartzman entitled “Cryogenic Engine Systems and Method.”) However, cryogenic engines have very high power densities and do not pollute the environment by burning any combustible fuel. Therefore, since high-pressure cryogenic expanders are very small, have power densities far higher than any internal combustion engine, generate very little sound, and produce no polluting exhaust products, cryogenic engines have been proposed for propelling road vehicles. (See the article, “Liquid Nitrogen as an Energy Source for an Automotive Vehicle,” Advances in Cryogenic Engineering, Vol. 25, 1980, pp. 831-837 by M. V. Sussman.) Unfortunately, liquified gas is much more expensive than gasoline and hence cryogenic engines are more expensive to operate than internal combustion engines. Although cryogenic engines operate by converting natural heat energy in the environment at ambient temperature into mechanical work at very high power densities, they are not cyclic heat engines. When the supply of liquefied working fluid at cryogenic temperature is consumed, the engine stops operating and must be re-filled with more liquefied gas working fluid. Since these engines operate by well-known thermodynamic processes according to the principles of thermodynamics, the expanded working fluid discharged from the last expander cannot be recondensed into a liquid at cryogenic temperature by conventional processes since there is no natural heat sink available at cryogenic temperatures to absorb the heat of vaporization that is required for achieving condensation. Since the cost of liquefied gas at cryogenic temperatures is very high, these prior art cryogenic engines are much more expensive to operate then internal combustion engines.
However, by designing a cryogenic engine with a working fluid such hydrogen that has a very high specific heat and very low critical temperature, recompressing the expanded gas isothermally at a sub-ambient temperature using an amount of mechanical work less than the amount of mechanical work generated from the expanders, and creating an artificial low-temperature heat sink to absorb the heat of compression of the isothermal compressor below natural ambient temperature by evaporating water, it will be possible to design a cryogenic engine such that the compressed working fluid always remains in the gaseous phase thereby enabling the engine to operate in a closed cycle at high power densities. But unlike all prior art cryogenic engines, this closed cycle cryogenic engine can convert an unlimited amount of natural heat energy at ambient temperature into an unlimited amount of mechanical work at high power densities without consuming any of its working fluid.
Since internal combustion engines used for propelling road vehicles generate huge amounts of toxic exhaust products harmful to all life and pollutes the environment, the closed cycle cryogenic engine disclosed herein provides a low cost alternative power source for propelling vehicles and generating electricity without generating any pollution. By increasing the size of the engine, they may also be used for generating bulk electricity in large power plants that presently operate by burning huge amounts of combustible fuel that generates toxic exhaust products or by operating nuclear reactors. Nuclear reactors generate extremely harmful radioactive waste products that can last for thousands of years. They are also subject to catastrophic accidents that can render huge areas of land uninhabitable. There is also the increasingly serious problem of “thermal pollution” that results from the necessity of having to absorb all of the rejected latent heat of condensation into the environment.
The cryogenic engine disclosed in the present invention is fundamentally and uniquely different from all prior art cryogenic engines in that the working fluid remains in the gaseous phase and operates as a closed cycle cryogenic engine. After the compressed low-temperature gaseous working fluid is heated by passing through a heat exchanger maintained in thermal contact with flowing atmospheric air at ambient temperature (which represents the engine's high temperature heat reservoir), it is isentropically expanded down to the sub-ambient temperature of evaporating water thereby converting a portion of the absorbed natural heat energy into mechanical work at very high power densities. By recompressing the gas at sub-ambient temperature isothermally by absorbing the heat of compression by evaporating water, the recompressed gas can be fed back into the heat exchanger to repeat the process in a closed cycle. Since the system can be designed such that the amount of mechanical work generated by the isentropic expander is greater that the amount of mechanical work consumed by the isothermal compressor, the net amount of mechanical work generated in each cycle will be positive. Barring mechanical breakdown, the engine will be able to extract unlimited amounts of natural heat energy from the environment at ambient temperature and convert it into unlimited amounts of mechanical work at high power densities for as long as the water supply lasts. Unlike prior art cryogenic engines, the working fluid is never consumed. The only fluid that is consumed is water that is available everywhere in unlimited amounts at no cost. Thus, the closed cycle cryogenic engine disclosed in the present invention represents a low-cost replacement engine for most internal combustion engines used for propelling vehicles and for generating electricity because it does not require burning any combustible fuel that is expensive and pollutes the environment, and because it operates at very high power densities.